There are numerous possibilities for applying cosmetic compositions onto the skin for skin care and body care. Creams, salves, and lotions are usually taken out of a jar, a tube, or a pump dispenser and applied and rubbed on by hand. Dimensionally stable stick compounds are wiped over the skin out of a stick dispenser until an effective quantity is applied. Gels and creams can also be applied using stick-like dispensers that are wiped over the skin with a dispenser surface. Numerous different application forms have been developed in particular for perspiration-inhibiting and/or deodorizing compositions for the armpit region; besides those already recited, these are chiefly the sprays that include and are free of greenhouse gases, and roll-on compositions. In the case of the latter, a slightly thickened liquid is applied from a reservoir container via a rotatably mounted ball, by rolling it over the skin. Numerous cosmetic active agents, among them the perspiration-inhibiting aluminum salts, are water soluble, and release thereof on the skin could be delayed by oil and fat constituents of the cosmetic. As an entirely aqueous product, however, the product would be almost impossible to dispense and thus would be unacceptable to the consumer. Slight thickening, however, allows such a composition to be used conveniently with a roll-on applicator. Polymeric thickening agents are often employed. A disadvantage here is that in the required concentrations, most polymeric thickening agents generate a very sticky skin feel. In addition, many of these thickeners have no additional cosmetic care-providing effects. Emulsions having a low oil and fat content represent an advantageous alternative to this. Emulsion formation already results in a rise in viscosity even without polymer thickeners, or with only small quantities thereof. The oil and fat portion of the emulsion furthermore provides a skin-care-providing effect.
Unlike microemulsions, emulsions are thermodynamically unstable. The thermodynamically stable microemulsions can usually be stabilized only by a relatively high emulsifier agent concentration. A high concentration of emulsifier agents, however, can in the least favorable case have a skin-irritating effect and is therefore avoided if at all possible. In addition, microemulsions often form only in a very narrow mixing range of the individual components. For cosmetic compositions having multiple constituents, it can therefore sometimes be very difficult in terms of development engineering to establish suitable microemulsion ranges. Emulsions are stable for a certain time because coalescence of the dispersed droplets is kinetically inhibited. This kinetic inhibition can be overcome by storage at high temperatures (relevant in particular for production and marketing in hot countries), or when stored in a context of large temperature fluctuations (e.g. in insufficiently climate-controlled sales areas, when transported over long distances). The high salt concentration in antiperspirant compositions, due to the relatively high concentration of perspiration-inhibiting active agents, can also promote emulsion destabilization (e.g. due to salting-out effects).
Typical antiperspirant roll-on emulsions are stabilized with polyethylene-glycol-including emulsifier agents, in particular with combinations of an emulsifier agent having a low HLB value, such as Steareth-2, and an emulsifier agent having a high HLB value, such as Steareth-20 or Steareth-21. The majority of the deodorant or antiperspirant roll-on formulations on the market having aluminum salts (aluminum chlorohydrates; aluminum zirconium chlorohydrates) in the form of oil-in-water emulsions include ethoxylated (=polyethylene-glycol-containing, PEG-containing) fatty alcohols or fatty acids as emulsifier agents, and propoxylated (=polypropylene-glycol-containing, PPG-containing) oils (usually ethers) as co-emulsifiers. As in other cosmetic sectors, opportunities for replacing EO/PO adducts (EO=ethylene oxide, PO=propylene oxide) are being sought in the deodorant and antiperspirant sector as well.